The quantitative determination of analytes in body fluids is of great importance in the diagnoses and maintenance of certain physiological abnormalities. For example, lactate, cholesterol and bilirubin should be monitored in certain individuals. In particular, determining glucose in body fluids is important to diabetic individuals who must frequently check the glucose level in their body fluids to regulate the glucose intake in their diets. While the remainder of the disclosure herein will be directed towards determining glucose, it is to be understood that the methods of this invention may be used for determining other analytes upon selection of an appropriate enzyme.
There have been various methods implemented in the past that use biosensors (e.g., biochemical sensors) to determine the quantity of a specific component (analyte) in a fluid sample. Some examples of these biosensors, including electrochemical sensors, are disclosed in U.S. Pat. Nos. 5,120,420, 5,264,103 and 5,620,579, and U.S. Publication No. 20010042683.
Some drawbacks with existing methods that use electrochemical sensors may occur when an insufficient amount of the fluid sample is present. These drawbacks occur when counter and working electrodes of the electrochemical sensors are not completely covered with the fluid sample, resulting in an incomplete current flowing across the electrodes. Since the amount of analyte (e.g., glucose) detected by the electrochemical sensor is directional proportional to the current flowing through the detection meter, failure to completely cover the electrochemical sensor's electrodes may result in a bias of the blood sample's analyte (e.g., glucose concentration).
It would be desirable to provide a method that detects when there is an insufficient amount of fluid sample and report such a condition as an error to the user. It also would be desirable to provide a method that detects electrochemical sensors with an abnormal rehydration process, because of an insufficient sample to completely re-hydrate the chemistry of the electrochemical sensor. It would be desirable to provide a method that determines an insufficient amount of fluid sample exists even when the electrodes of the electrochemical sensors are sufficiently covered. It would also be desirable to report such conditions as errors to the user if the bias of the analyte concentration exceeds a predetermined threshold caused by, for example, solution movement in incompletely filled sensors or abnormal re-hydration kinetics.